Here is the attestation for verse 14:34 in Marcion
1) Epiphanius Panarion 42.146
Greek text
<ιε> <καὶ> <κγ> <σχόλιον>. «
Αἱ γυναῖκες ἐν ἐκκλησίᾳ σιγάτωσαν·
οὐ γὰρ ἐπιτέτραπται αὐταῖς λαλεῖν,
ἀλλὰ ὑποτασσέσθωσαν,
καθὼς καὶ ὁ νόμος λέγει».
<ιε> <καὶ> <κγ> <ἔλεγχος>. Εἰ κατὰ τὸν νόμον διατάσσεται ὁ ἅγιος τοῦ θεοῦ ἀπόστολος τὴν εὐταξίαν τῇ ἁγίᾳ τοῦ θεοῦ ἐκκλησίᾳ, οὐκ ἄτακτος ὁ νόμος, ἀφ' οὗπερ τὴν εὐταξίαν μετακομίζεται οὐδὲ ἀλλοτρίου θεοῦ ὑπάρχει ὁ νόμος, τὴν γυναῖκα καθυποτάξας τῷ ἀνδρί. συναρέσκει γὰρ καὶ τῷ ἀποστόλῳ τοῦτο ἐν τῇ τῆς ἐκκλησίας νομοθεσίᾳ, ὥς φησι· «καθὼς καὶ ὁ νόμος λέγει». ποῦ δὲ εἶπεν ὁ νόμος ἀλλὰ ἐν τῷ εἰπεῖν τὸν θεὸν πρὸς τὴν Εὔαν εὐθύς «πρὸς τὸν ἄνδρα σου ἡ ἀποστροφή σου καὶ αὐτός σου κυριεύσει»; εἰ γὰρ καὶ ἐν ἄλλοις τόποις, ἀλλὰ ἐντεῦθεν ἡ ἀρχή. εἰ τοίνυν ἀπὸ τότε ἡ γυνὴ ὑπετάγη ἐκ προστάγματος θεοῦ τῷ ἀνδρὶ καὶ ἀκολούθως ὁ ἀπόστολος καθυποτάσσει ταύτην, οὐκ ἀντιθέτως τῷ ποιήσαντι τὸν ἄνθρωπον καὶ τὴν γυναῖκα θεῷ καὶ αὐτὸς κελεύων δείκνυσιν ἐξ ἅπαντος ὅτι τοῦ αὐτοῦ [θεοῦ] ὑπάρχει ὁ ἀπόστολος νομοθέτης θεοῦ, οὗ καὶ ὁ νόμος ἦν καὶ ἡ πᾶσα παλαιὰ διαθήκη, καὶ τοῦ αὐτοῦ ἡ καινὴ διαθήκη, τουτέστιν αἱ δύο διαθῆκαι, αἱ τὴν γυναῖκα τότε καὶ νῦν καθυποτάξασαι τῷ ἀνδρὶ δι' εὐσεβῆ καὶ ἀντίρροπον εὐταξίαν.
English (from
https://books.google.com/books?id=IKyxt ... on&f=false go to page 352:
Scholion 15 and 23. "Let your women keep silence in the church; for it is not permitted unto them to speak, but they are commanded to be under obedience, as also saith the Law."
(a) Elenchus 15 and 23. If God's holy apostle enjoins good order on God's holy church on the Law's authority, then the Law from which he took the good order is not disorderly; nor is the law of a foriegn God because it subjected wife to husband. For this was satisfactory to the apostle too in his legislation for the church - as he says, "as also saith the Law."
(b) And where did the Law say so, but when God said at once to Eve, "They resort shall be to thy husband, and he shall rule over thee?" For even though it is also found in other passages the original statement of it is here.
(c) Now if the wife was declared subject to the husband from then on by God's ordinance - abnd if the apostle subjects her accordingly, and not in disagreement with God who made husband and wife, then the apostle too, by commanding it, show decisively that he is a lawgiver for the same God to whom both the Law and the whole Old Testament belong, and that the New Testament is the same God's as well - that ism the two Testaments, which then and now subjected wife to husband for the sake of an equivalent godly order.
Epiphanius makes the mistake here of assuming verse 14:35 is present as well, even though it is not attested (clearly he compiled a list from some sources of known NT passages of the Marcionite text). Verse 14:35 is used by Epiphanius to tie the wife to the husband and then proceeds with his scholasticism to harmonize the Marcionite to the Old Testament. His logic collapses if verse 14:35 is not present, which IMO it was not
2) Dialogue Adamantius 2.18 (English Robert A. Pretty), although it is the Catholic champion Adamantius speaking, he makes it clear he is quoting the Marcionite text (well as reliable as DA ever gets when Adamantius speaks):
... The wretch Marcion, although he corrupted the statements of the apostle did not completely erase them, but these people (i.e., Marcionites) right up to the present (written ~300 AD) remove anything that does not agree with their opinions. So whatever it may be that they do not understand, and have abandoned because it opposes their views -- all this I have gathered up (like small grapes left for gleaners) from the apostolic and prophetic utterances, and I will clearly expound it for your understanding. the Apostle speaks thus, "Let the women keep silence in Church; for permission has not been given for them to speak, but to be subordinate, as also the Law says" ...
Ὁ γὰρ σχέτλιος Μαρκιων, ῥαδιουργήσας τὰ κατὰ τὸν ἀπόστολον, οὐ παντάπασιν ἀπήλειψε, καὶ οὗτοι μέχρι τοῦ δεῦρο περιαιροῦσιν ὅσα οὖν μὴ νοήσαντες κατέλειψαν ἑαυτοῖς ἐναντιούμενα, ταῦτα ὥσπερ ἐπιφυλλίδας ἀναλεξάμενος ἐκ τῶν ἀποστολικῶν καὶ προφητικῶν φωνῶν, προφανῶς τῇ σῇ συνέσει ἐπιδείξομαι. λέγει δὲ οὕτως ὁ ἀπόστολος·
αἱ γυναῖκες ἐν ἐκκλησίᾳ σιγάτωσαν, οὐ γὰρ ἐπιτέτραπται αὐταῖς λαλεῖν, ἀλλ᾽ ὑποτάσσεsθαι. καθὼς καὶ ὁ νόμος λέγει.
Rufinus Latin:
Infelix enim Marcion, cum adulterasset scripturas, apostoli codicem non est ausus in omnibus uel falsare uel etiem delere; sed isti etiam nunc quae eis uisa fuerint auferunt, id est ea quae assertionibus suis uidentur esse contraria, et sola derelinquunt quae aduersa sibi non intellexerunt. Haec ergo ego uelut racemos quodam ab istis pessimis uindemiatoribus derelictus de apostolicis et euangelicis uocibus colligens, etiam ex ipsis ut se habeat ueritas approbabo. Itaque dicit apostolos: Mulieres in ecclesia taceant. Non enim permittitur eis loqui sed subditas esse, sicut et lex dixit.
note: Marcion reads ⌐ ἐκκλησίᾳ for ταῖς ἐκκλησίαις (ecclesia for ecclesiis) 119 330 2400 syrP Cop Eth OL:KI, similar for ἐπιτέτραπται which makes me suspect a common corrupted anti-Marcionite source for Panoranion and Adamantius texts
Tertulllian only mentions 14:34 in passing AM 5.8.11, although he covers exactly the same points. but he refers back to 11:5-6 to show that women's prophecy is still allowed provided they be veiled (11:10) as showing Marcion also allowed this.
Aeque praescribens silentium mulieribus in ecclesia, ne quid discendi duntaxat gratia loquantur … ex lege accipit subiciendae feminae auctoritatem;
In precisely the same manner,[ Æque] when enjoining on women silence in the church, that they speak not for the mere sake [Duntaxat gratia] of learning (although that even they have the right of prophesying, he has already shown [1 Corinthians xi.5, 6] when he covers the woman that prophesies with a veil), he goes to the law for his sanction that woman should be under obedience.
Tertullian unlike Epiphanius does not tie verse 14:34 to verse 14:35, which is not present in any of the accounts. He makes the same claim as Epiphanius, by ignoring the "καὶ" so he can make the Law the primary motivation, rather than a "by the way" clause.
As attestation goes this is some of the strongest for any verse in the Marcionite collection.